The present invention relates to an improved stuffing box assembly for the sliding joint between the piston (ram) and cylinder of the hydraulic ram portion of a hydraulic press such as a hydraulic injection molding machine for molding articles from resin. One aspect of the invention provides a sliding bearing supported between the gland and the ram. An aspect of the invention relates to an improvement of the foresaid having a liner bearing material selected from the class consisting of thermosetting and thermoplastic resin. One aspect of the invention is an improved stuffing box assembly for the sliding joint between the piston and the cylinder of the hydraulic ram unit in a horizontally disposed hydraulic injection molding machine, and the combination therewith, in connection with which the invention will be described.
Hydraulic injection molding machines for molding articles and products of synthetic resin are characteristically arranged to operate on a horizontal axis and to hydraulically close and hold closed the mold portion. Also, characteristically, one of the mold portions is mounted on a fixed platen through which the injection unit is connected to deliver molten plastic into the mold cavities. The other mold part is characteristically mounted on a moving platen suspended from tie rods along which it slides. The moving platen is actually reciprocated by the ram of the hydraulic ram part of the system.
The ram is usually of quite large diameter and weight, e.g. 13.62 inches and 1,560 pounds on a machine exerting 150 tons clamping force, 21.75 inches and 6,600 pounds on a machine exerting 500 tons clamping force, and 30.25 inches and 4,000 pounds on a machine exerting 1000 tons clamping force.
The present invention is addressed to the stuffing box which seals between the ram and hydraulic cylinder. This particular joint has in the past leaked due to such factors as: the pressures that must be resisted in building up the clamping tonnage of the machine; sticking or "stiction" requiring increased force or tonnage to open an injection mold after a molding operation; possible damage to the ram from nicks, galling and scoring; and entry of contaminants including dirt particles, and the like, into the packing due to inadequate wiping of the ram. The size and weight of the ram being handled aggravate problems encountered in assembling and maintaining such a system.
Accordingly, it is one objective of the present invention to provide an improved stuffing box assembly for a hydraulic injection molding machine for molding articles from resin and/or more broadly to provide the same for a hydraulic press.
An objective is to provide an improved packing retainer assembly for a stuffing box on a hydraulic injection molding machine.
Accordingly, the present invention contemplates the combination with a hydraulic injection molding machine for molding articles from synthetic resin of a stuffing box at the hydraulic ram portion thereof to enhance the sealing and wiping of the sliding joint between the ram and cylinder there. Such a stuffing box has packing disposed therewithin in an annular outer recess at the end of the cylinder in engagement with the ram and of the kind which expands radially inward against the ram in response to axial compression by a gland or packing retainer ring. The invention in such context further comprises a pilot means to obtain concentricity connected between the gland and stuffing box and preferably comprising a pilot shoulder or hub protruding from the gland to within the stuffing box, a support bushing groove on the inside diameter of the gland and a support bushing supported in the groove and having an inside diameter less than the inside diameter of the gland. The support bushing is preferably made of a synthetic resin and even more preferably made from a fiber reinforced synthetic resin. The resin preferably is selected from a class consisting of Teflon (tetraflouroethyline resins and flourinated ethyline-propylene resins) and phenol formaldehyde or more broadly thermoplastic and thermosetting resins. Again, preferably, the resin is fiber reinforced with linen, cotton, wool, or other nonabrasive cellulosic and keratin fibers.
The invention also contemplates a stuffing box constructed as aforesaid for use in a hydraulic ram portion of a hydraulic press preferably in a hydraulic injection molding machine.